1. Field of the Invention
The present invention relates generally to a system for monitoring the combustioning condition of an internal combustion engine of an automotive vehicle. More specifically, the invention relates to a combustioning condition monitoring system for a multi-cylinder internal combustion engine.
2. Description of the Background Art
In the recent years, there has been developed various engine combustioning condition control systems for maintaining optimum engine combustioning condition for achieving high fuel efficiency and drivability. In order to monitor the engine combustioning condition, a combustioning gas pressure in an engine combustion chamber, which pressure may be hereafter referred to as cylinder pressure, has been monitored. For example, a technology for detecting the engine combustioning condition has been disclosed in Japanese Utility Model First (unexamined) Publication (Jikkai) Showa 62-24037. This publication proposes the technology monitoring of the engine combustioning condition by means of a pressure sensor formed in a form of a washer to be mounted onto the engine cylinder block with a spark ignition plug as a washer therefor. Such a pressure sensor monitors the internal pressure in the combustion chamber for producing a charge corresponding to the combustioning condition in the associated engine cylinder.
Such prior proposed technology is costly because it requires separate pressure sensors for the respective engine cylinders. Furthermore, as can be aware of, since the internal pressure in the engine cylinder during low engine load condition, such as engine idling condition, high accuracy in monitoring the internal pressure of the engine cylinder cannot be expected. Furthermore, since engine knocking tends to be caused in the vicinity of the top dead center in piston compression stroke. When the engine knocking is caused, the output of the pressure sensor may be influenced by the knocking vibration of the engine block, causing an error in detection of the internal pressure in the engine cylinder and fluctuation of engine revolution.